Level Switches

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Level switches are applied in a wide range of industries. Some examples include pharmaceutical ingredients processing, for the measurement of bulk quantities of drug ingredients; food and beverage processing, for the monitoring of liquid and powder food item levels during production and packaging; HVAC systems design, for control and level monitoring of oil or refrigerant levels in heating and cooling systems (chambered level switches are often used in boilers); industrial manufacturing, to control potentially hazardous chemicals required in various processing applications; and municipal or industrial water treatment, for the monitoring of wastewater levels. Mechanical level switches, such as float level switches, displacer level switches and rotary tank level indicators, come into direct contact with the materials they measure and can be used as both solid and liquid level switches. Non-mechanical level switches, such as capacitance level sensors, ultrasonic level sensors and optical level switches, do not come into direct contact with the materials they measure.

The basic construction of level switches includes a switching mechanism, a tube and a couple of areas of connection. However, the design varies widely based on the desired application, what materials the switch is going to be used to monitor, the size of the container and other considerations. In particular, designs can vary for simple to complex and can be triggered by pressure, temperature or buoyancy. Additional features of level switch devices include thermal sensors, vibrating sensors and optical sensors, which can be modified to recognize specific substances or to reveal when a certain viscosity, density, opacity or thermal conductivity condition is reached. For construction, level switch manufacturers commonly use materials such as stainless steel, brass and various types of plastics. The two most common plastic materials used include polypropylene and polysulfone, which are available in different colors, and which are good choices for acidic conditions, such as in electroplating and metal cleaning. They are also useful for lower-temperature food processing applications and for general-purpose applications in commercial or consumer appliances and equipment. Brass sensors and switches can be used in petroleum-based liquids; they can be installed in storage tanks of vehicles, generators, and transmission and hydraulic systems as well as in lubrication, recovery, refining and fuel processing equipment. Level switch manufacturers can also cater to specific applications.

While there is a diverse range of devices that fall under the heading of level switches, there are those that are more commonly used for industrial applications. Some of these more popular level switch devices include capacitance level sensors, chambered level switches, displacer level switches, float level switches, optical level switches and ultrasonic level sensors. Capacitance level sensors function to indicate the presence of materials, particularly as they reach a particular level. Capacitance level sensors can be used to measure the level of materials such as aqueous and organic liquids, solids and slurries. Chambered level switches are enclosed in a casing, referred to as a chamber, which surrounds the switch mechanism. Although they are used primarily to monitor the amount of liquids and various other materials in containers, chambered level switches can be used to control the flow of materials into and out of containers as well. Displacer level switches monitor and measure changes in buoyancy force that are placed on a displacer by allowing for adjustments to the level of measured materials.

Level switch configurations range widely in terms of their configurations. In the case of the simplest liquid level switches, the position of a float or buoy is influenced by the level of the materials the float is intended to measure. If the level of the material rises enough, it will cause the float to rise as well. When the float reaches a certain point, it causes an electrical circuit within the level switch to become closed, sending a signal to whatever indicators or control equipment to which the switch may be attached. A similar principle of operation applies also to solid level switches. Spinning rotary level switches, which involve paddles or blades that rotate around an axis, are used to measure the levels of granular solids. Such switches can be placed at different elevations within a storage enclosure. When the spinning of a rotary level switch is interrupted by the presence of a solid, that interruption indicates to control equipment that the level has reached whatever elevation at which the switch has been placed. Level switch design becomes more complicated from there; it can involve the transmission and reflection of ultrasonic waves, the projection of infrared beams and the transmission of radio waves. Correctly pairing a level switch variety with its application results in an effective and accurate materials measurement system. 

Level Switches and Level Switch Manufacturers Images Provided by SOR Inc.

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Level Switches Types

• Capacitive level sensors are able to channel or collect a charge of electricity.
  
• Chambered level switch designs include encasings, or chambers, that surround the sensor or switch mechanisms. Chambers can be flanged or sealed to offer protection or hermetic air-tightness.
  
• Displacer level switch devices are affected by buoyancy force changes on a weight (displacer) heavier than the liquid. Through a spring mechanism, the suspended weight is attached to an attraction sleeve that moves into or out of a magnet field, thus actuating or deactuating the switch.
  
• Electric level switches contain open or closed contacts that indicate the presence or absence of liquid.
  
• Electromechanical level switches work with a combination of electric and mechanical parts.
  
• Float level switch mechanisms can most simply be a rod floating in a liquid that is raised until a pump, an indicator, an alarm or other device is activated. It could also be a mercury switch enclosed in a hinged float, a suspended "bobber" attached to an attraction sleeve that actuates a magnet field or a more complex sensor construction.
  
• Hydrostatic level switches are sensitive to the static, or stationary, water pressure acting on them.
• Level control switches are used specifically for material low control, ensuring that levels remain within a specific, designated range.
• Level indicators are measurement devices that determine the amount of material that is in a container.
• Level sensors are measurement devices used to determine the level of materials such as liquids, powders, slurries and granular materials.
• Liquid level switch constructions monitor the amount of fluid in a vessel. Ultra-low liquid level switches are available to detect very low levels for early indication of a liquid presence and effective use of expensive liquids.
  
• Mechanical level switch designs offer versatility and rugged, industrial constructions relying on buoyancy principles and made of floats or displacers, spring mechanisms, attraction sleeves, optional chambers and magnet fields that activate switching mechanisms.
  
• Microwave level switches are made up of two separate parts, a transmitter and a receiver. The transmitter emits a burst of energy at approximately 200 times a second toward the receiver; a substance interruption of the microwave between the two devices is the trigger.
  
• Multi-point switches can be engineered to provide a number of actuation points.
  
• Optical level switches are cost-effective, compact, quickly installable options that contain no moving parts but use LEDs, which transmit infrared light. When a translucent liquid meets the point where the light contacts the prism, the light is reflected into the water and does not allow the photo transistor to energize.
  
• Pneumatic level switches are air-pressure activated through valves and amplifiers.
• Tank level indicators are a type of level switch that is specifically utilized within tanks, which are large vessels used to hold gases or liquids as well as free-flowing solids.
• Thermal level switches include temperature sensors that provide activation when a heat change occurs as the liquid surrounds them. Some can sense the difference between the temperatures of the air space and the liquid.
  
• Two-stage level switch devices are designed with a flood-preventing capability. If liquid reaches the second stage, the switch will turn the pump off and/or sound an alarm.
  
• Ultrasonic level sensors utilize high-frequency (above the audible level) pulse wave technology.
  
• Vibrating level switches can come with reed, probe or tuning fork sensors, which all have similar constructions of a driver coil that vibrates a paddle. The switch detects a dampening of the vibration when the sensor is surrounded by a substance.

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Level Switches Terms

Aperture - The space between contiguous parallel wires, expressed in millimeters.
 
Buoyancy - An object's upward force produced by the fluid in which it is fully or partially submerged.

Mercury Switch - A sealed glass tube containing a minimal amount of liquid mercury and two unconnected electrodes that produce electricity flow when the tube is moved past a certain angle so that the liquid metal pools in between the electrodes, making a complete circuit. Once back in the original position, the current stops instantly.

Opacity - The extent to which something is optically non-transmissive; opacity is the opposite of transparency.

Polypropylene or polypropene (PP) - A thermoplastic polymer that is rugged and unusually resistant to many chemical solvents, bases and acids.

Polysulfone or PSU - A polymer thermoplastic material that offers toughness, rigidity, high-strength and transparency, while also maintaining its characteristics between negative 100°C and positive 150°C.

Sluice - A water channel with a gate used to regulate levels and flow rates in rivers, canals and wastewater treatment plants, and to retrieve minerals during the mining process.

Viscosity - The thickness of a liquid, or its resistance to flow.

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